1. Field of the Invention
The present invention relates generally to a multiple task control system for an automotive vehicle, which performs a plurality of mutually independent controls, such as traction control, anti-skid brake control, suspension control and so forth, employing at least one control parameter common to the other. More specifically, the invention relates to a fail-safe system for such multiple task control system.
2. Description of the Background Art
In automotive technologies, various electronic control systems have been developed for enhancement of vehicular drivability, driving stability, safety, riding comfort and so forth. For performing various controls, it is not practical to provide a plurality of microprocessors for independent operations to each other in view of cost and strictly limited space for installation. Therefore, it is practical to combine more than one control function to perform on a single microprocessor. For example, Japanese Patent First (unexamined) Publication (Tokkai) Showa 61-169211 discloses a multiple task control system performing an anti-skid brake control and a driving power or torque distribution control for four-wheel drive vehicle. The disclosed control system controls anti-skid actuator which adjusts braking pressure in a wheel cylinder. Also, the disclosed control system controls a torque distribution control clutch for adjusting driving torque distribution between primary and subsidiary driving wheels. The control system employs a wheel speed sensor for monitoring rotation speed of a road wheel as a common sensor for providing control parameter data for both of the anti-skid control and the driving torque distribution control.
For such control system, fail-safe functions are provided for undertaking respectively associated control when failure is caused in associated one of control functions. Typically, individual fail-safe functions are provided for respective control functions for independent operation to each other. In such case, action of the fail-safe function for one control function can interfere or affect the other control function.